The present disclosure relates generally to Light-Emitting Diode (LED) lighting systems, and more particularly to Alternating Current (AC) driven LED lighting systems and control methods that efficiently provide an operating voltage.
Light-Emitting Diodes or LEDs are increasingly being used for general lighting purposes. In one example, a set of LEDs is powered from an AC power source and the term “AC LED” is sometimes used to refer to such circuit. Concerns for AC LED lighting systems include manufacture cost, power efficiency, power factor, flicker, lifespan, etc.
FIG. 1 demonstrates an AC LED lighting system 100 in the art. The AC LED lighting system 100 employs full-wave rectifier 18 to rectify an AC voltage VAC and provide a DC input voltage VIN at an input power line IN and a ground voltage at a ground line GND, where the ground voltage is deemed to be 0 volt in this system. A string of LEDs are segregated into LED groups 201, 202, 203, and 204, each having one or more LEDs. An integrated circuit 102 performing as a LED controller has pins or channel nodes PIN1, PIN2, PIN3, and PIN4, connected to the cathodes of LED groups 201, 202, 203, and 204 respectively. Inside integrated circuit 102 are path switches SG1, SG2, SG3, and SG4, and a current controller 103 as well. When the input voltage VIN at the input power line IN increases, current controller 103 can adjust the conductivity of path switches SG1, SG2, SG3, and SG4, making more LED groups join to emit light. Operations of integrated circuit 102 have been exemplified in U.S. Pat. No. 7,708,172 and are omitted here for brevity.
There in FIG. 1 includes a low dropout linear regulator (LDO) 112, which drains current from input power line IN to charge capacitor COUT, so operating voltage VCC is built up at a power source line VCC for powering integrated circuit 102 or other integrated circuits, such as microcontroller units. The LDO 112 is power consuming, however. The voltage drop across the LDO 112 could be as high as several hundred volts, so the power consumed by the LDO 112 will become significant.